slipper launch

Discussion in 'Boat Design' started by BIG MAC, Aug 3, 2004.

  1. BIG MAC
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    BIG MAC Junior Member

    slipper launch - WITH IMAGES THIS TIME!

    We are starting design of a slipper launch with lines based on the classic Thames river boats but power/speed of modern runabouts. Multipurpose daycruise, picnic, show-off, and water ski boat. image of a restored slipper attached. the original concept was to use the hull design of a mahogany runabout and modify chine, sheer, and engine/cockpit arragnement - keeping the weight distribution correct as there is no room for error when the transom free board is only 4" . taking advantage of tried and true mahogany runabout plans and power setups would give us a good starting point.

    We found drawings of a genuine article, a Wargrave Slipper and are considering using the Wargrave hull (drawing atttached).

    what are opinions about the keel?

    does anyone have a source for a long shaft log as would be needed and low angle strut?

    We've built strip hulls and ply on frames and stringers but are considering stitch and glue. Is 26' with a v8 still in the realm of stitch and glue?

    thanks so much for the input.

    Jim
     

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    Last edited: Aug 3, 2004
  2. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Ah-yup! :)
     
  3. Willallison
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    Willallison Senior Member

    flick the idea of modifying your existing slipper plans - what you really need is to modify the sheerline of an appropriate runabout to give the required appearance. The structure required to support a 5 knot riverboat are far different to those for a 30 knot speedboat. Also the bottom shape of the slipper isn't right - you need a planing hullform. Then there's the weight distribution - whack a V8 up front and your centre of gravity is going to be too far forward...begs not be onboard when you accelrate to 25 knots for the 1st time... ;) ....getting the gist yet?
    Having said that, I like the idea - I've toyed with doing something similar myself on the odd occaision
     
  4. cgorton
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    cgorton Junior Member

    I agree with Willallison. I've seen classic hull forms that get re-powered with dangerous results. The fore-foot of the launch you show is deep and the center of buoyancy is well forward. At speed, this will cause some serious steering issues.
    Also, the faster you push a boat, the farther aft you need the CG to be. Putting a modern engine where the existing one is would be a mistake.
    Further, long keels like that don't work well at speed. They're unnecessary and can cause dynamic problems.
    That being said, you may be able to re-design the boat below the waterline to accomodate more power and higher speed.

    Craig
     
  5. SailDesign
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    SailDesign Old Phart! Stay upwind..

    I agree with Will, too. But...
    Long keels like that are fine at speed if the rest of the boat suits. Just ask any lobsterman :)
    My chief worry, assuming you can resdesign the beast for higher speed, would be the structure of the stern. All it would take is one small wake and you're likely to rip off that cute little ar... tail she has :)

    How 'bout this idea - scanned from Colin Mudie's "Power Yachts" without permission, hopefully without lawsuit.


    Steve
     

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  6. BIG MAC
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    BIG MAC Junior Member

    well taken -

    getting the engine out of the cockpit and off the stern is an integral part of the concept. we also run out of deck clearance if we move it back. We put a chris craft type runabout bottom it - it gets rid of the deep bow sections but surprisingly only moved the cb 15" aft. the cb was about the back of the transmission - now it is under the driver. this will help weight distribution as the big empty bow sections have to be delt with. the originals put the tank up high in the bow. not a good place for all that weight.

    the engine up front took a minute to get used to. but, weight is weight and the hull doesn't know what causes it, whether it is from engines or people - just that it is there. youi can look at this as swapping driver/passenger weight with engine weight. granted, we are swapping a 900#engine for 350# of people but it's not as radical according to the math as it is according to the eye.

    thanks for the input! all is appreciated.
     
  7. BIG MAC
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    BIG MAC Junior Member

    a "classic" foiler?

    now that's a mix of technologies and styles! i'm getting hands-on experience with foils. bought and air chair on ebay and am trying to master the beast. one day i will realize i'm not 20 years old any more. i told them to keep it slow and don't pull me over 20 mph until i learn to control it. i've broken my foot on it and pulled lower back muscles so far. decided to download the instructions - you are supposed to learn at 8-12 mph, not 20! looking forward to being healed so i cn have another go at it. the point is, being on foil ski really gives you an intuitive feel for how they really work. it's very surprising.

    the structure at the stern winds up performing as a box beam. the weakest point on this one is amidships where where is no deck to complete the structural diaphram. still plenty strong.

    thanks for your reply!
     
  8. cgorton
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    cgorton Junior Member

    I still disagree with the keel. Most lobstermen I know use rounded bilges and operate at speeds under that of a modern (planing) waterski boat. In fact, when you consider pulling a skier at 32mph (a recreational number, 36 is tournament level) you'll need not a little power. Now take away the skier- the boat will most likely be operating at almost 40mph. That keel will do things to a light boat in a turn that are not desirable. So why bother with it? I can't think of any boat that goes nearly 40mph with a keel forward of the CB.
    A little off topic, but when I was learning to windsurf I found that the daggerboard becomes undesirable once you plane out. It makes it impossible to carve a turn.
    But, I love seeing great looking boats get attention, so do keep us posted!

    Craig
     
  9. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Craig,
    If you look at a lobsterboat, you'll notice that "yes", the bilges are round, but there is also a great long keel down there. Some of these boats regularly exceed 30 knots (I forget the record for the racing guys, but it's well over 50 knots) in the course of the day, and the keel is just fine. Power? Ah-yup! Last one I looked in had a Volvo 650hp powerplant. Should oughta give him 40 knots.

    Steve
     
  10. Willallison
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    Willallison Senior Member

    ...true - but what happens when the skipper's the only one on board?
    From what you've said, you're basically heading down the path that we're all suggesting - a runabout that looks like a slipper. I'd still have reservations about the engine location and I'm sure that with a little bit of clever styling, you could mimmick the looks and still run a mid-mount. The other alternative, of course is to move the cockpit further aft, but then you wind up with a different boat altogether.....
     
  11. Corasco
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    Corasco Kit

    Slipper Launch plans

    I want to build a traditional slipper launch using traditional methods, not a stich a glue plan. I just did much ot the Thames Walk in England and fell in love with those boats; we can use one here on the Missipssippi.

    Does anyone have access to correct and original drawings that I can use?
     
  12. Elmo
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    Elmo Junior Member

    http://www.selway-fisher.com/McClassic.htm#HENLEY

    Not aware of any traditional original plans that are available.
    Not to say they don`t exist....

    With the Fisher plans ,you would need to install chine logs and frames ...somewhat "reverse" building...if you want traditional.
    Should not be too difficult.
     
  13. Corasco
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    Corasco Kit

    Kit

    See Big Mac's photo and drawing at the top of this thread and maybe he knows where such drawings and plans exist?
     
  14. Elmo
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    Elmo Junior Member


  15. Corasco
    Joined: Dec 2009
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    Corasco Kit

    Kit

    I did e-mail him but have not heard back yet. Any other suggestions for web sites with plans or books that might have such? I have also e-mailed some folks in England but have heard nothing.

    Thanks.
     
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